DE-A-4027126 describes membrane modules comprising pockets which are arranged in parallel. These modules consist of a box-shaped housing in which the membrane pockets, whose outer dimensions correspond to the inner housing dimensions, are arranged. Between the membrane pockets, along the lateral edges, there are rod-shaped spacer elements which define a certain distance between the membrane pockets. The membrane material may additionally have prominences or reinforcements, which ensure that a certain distance between two membrane pockets is ensured over the entire surface. Each membrane pocket is provided with a supply tube and a discharge tube which go into one common supply and discharge tube. The membrane material used is gas permeable and liquidproof. Preferably a polyurethane film is used.
If such a membrane module is used, for example, as a means for flue gas purification, considerable membrane surface is needed. To make the process economical, manufacturing expense must be minimized. Connecting each pocket with its separate supply and discharge tube is time consuming, complicated and failure-prone. Another shortcoming is the fact that the membrane pockets bulge with the weight of the liquid in the pockets and thus reduce the cross-section which is free for gas permeation. The exact flow resistance is very difficult to calculate because it varies with time.
When the lateral surfaces of the membrane pockets are provided with prominences, the membrane becomes more expensive to produce and the efficiency of the substance exchange through the membrane is reduced.
Since the membrane pockets are held only laterally, the flexible front edge may turn back under the accumulated dynamic pressure of the gas Flow and clog adjacent interstices which were intended for the passage of gas.
Considering the various opportunities to use such modules, such as in flue gas purification, there is a need for a membrane module of simple design which can be economically manufactured and which is designed such that it ensures defined substance exchange conditions also over long operation times.